The present invention relates to brake pressure control mechanisms for electrically controlled braking systems. It finds particular application in conjunction with an anti-lock braking system (xe2x80x9cABSxe2x80x9d) and will be described with particular reference thereto. It will be appreciated, however, that the invention is also amenable to other like applications.
Vehicles equipped with an ABS are becoming more common. ABS""s typically cycle through three (3) phases, including (1) building, (2) holding, and (3) exhausting pressure in a brake chamber, to control the braking action. A solenoid valve within the ABS is controlled electronically to selectively achieve one of three (3) positions. Each position of the solenoid valve corresponds to one (1) of the three (3) respective phases of the ABS.
The solenoid valve includes a supply port, an exhaust port, and a delivery port. Electrical coils surround a magnetic armature core within the solenoid. The armature core is positioned within the solenoid valve as a function of current passing through the electrical coils. The coil current is determined by control signals generated within the ABS. The three (3) ports are opened and/or closed independently of each other, to achieve the three (3) phases of the ABS, as a function of the armature core position.
ABS applications must be capable of switching between building, holding, and exhausting pressure in the brake chamber very quickly. Consequently, the valves used in the ABS applications must quickly switch among the three (3) states.
Two (2) different types of solenoid valves (i.e., pneumatic piloted valves and direct drive valves) are commonly used in ABS applications. Pneumatic piloted valves use electricity to activate the pilot pressure that, in turn, controls the pressure in the brake chamber. However, pneumatic piloted valves usually have more components and more complicated structures relative to direct drive valves. Therefore, pneumatic piloted valves are typically more difficult and more costly to manufacture than direct drive valves. One drawback to direct drive valves, however, is that they require larger electrical coils to drive their armature cores in order to build, hold, and exhaust the pressure in the brake chamber. This is especially true in 12 volt direct-current (xe2x80x9cVDCxe2x80x9d) environments, which are typically available in vehicles incorporating ABS. For this reason, pneumatic piloted valves are often used instead of direct driving valves for ABS applications in vehicles.
The present invention provides a new and improved apparatus and method which overcomes the above-referenced problems and others.
An electrical driver circuit for a cantilever solenoid valve includes a first electrical switching device for converting a first logical control input signal into a first valve control output and a second electrical switching device for converting a second logical control input signal into a second valve control output. Third and fourth electrical switching devices are controlled as a function of the first valve control output produced by the first switching device. Fifth and sixth electrical switching devices are controlled as a function of the second valve control output produced by the second switching device. A voltage potential difference is created between a first electrically common point, defined between the third and fourth switching devices, and a second electrically common point, defined between the fifth and sixth switching devices, as a function of the logical control input signals.
In accordance with one aspect of the invention, the first and second electrical switching devices each includes a collector electrically connected to an electrical power source and an emitter electrically connected to a ground.
In accordance with a more limited aspect of the invention, respective control inputs to the third and fourth switching devices are electrically connected to the collector of the first switching device. Also, respective control inputs to the fifth and sixth switching devices are electrically connected to the collector of the second switching device.
In accordance with a more limited aspect of the invention, the third and fourth switching devices each includes a collector and an emitter. The collector of the third switching device is electrically connected to the power source. The emitter of the fourth switching device is electrically connected to the ground. The first electrically common point is created by electrically connecting the emitter of the third switching device to the collector of the fourth switching device. The fifth and sixth switching devices each includes a collector and an emitter. The collector of the fifth switching device is electrically connected to the power source. The emitter of the sixth switching device is electrically connected to the ground. The second electrically common point is created by electrically connecting the emitter of the fifth switching device to the collector of the sixth switching device.
One advantage of the present invention is that a xe2x88x9212 VDC to +12 VDC differential voltage range is supplied to the solenoid valve using only a single +12 VDC power source.
Another advantage of the present invention is that, because at most only one-half (xc2xd) of the driver circuit is energized at a single time, the driver circuit is relatively energy efficient.
Another advantage of the present invention is that fast-switching is achieved between build, hold, and exhaust phases of a solenoid valve.
Still further advantages of the present invention will become apparent to those of ordinary skill in the art upon reading and understanding the following detailed description of the preferred embodiments.